III. PHYSICAL AND VEGETATIONAL ASPECTS OF THE SAHARA
107
B. GEOLOGIC HISTORY
1. Geologic Boundaries
Geologically, the Sahara is bounded to the north by a large accidental
tectonic feature, stretching out from Agadir to the Gulf of Gabès, and to
the south by the valleys of the Senegal and of the Niger. A great number
of works relative to the geological study of the Sahara has been published*
(Kilian, 1922, 1925; Joléaud, 1938; Bernard, 1939; Monod, 1935, 1945;
Hernandez-Pacheco and Hernandez-Pacheco, 1942; Hernandez-Pacheco et
a/., 1949; Lelubre, 1952; Menchikoff, 1930, 1957; Pareyn, 1962; Freulon,
1964; Rognon, 1967; Furon, 1964, 1968; Conrad, 1969; Caby, 1970).
2. Relief of the Sahara
According to Menchikoff (1957): "The Sahara is a typical example of
a region of continental platform, composed of a Precambrian metamorphic subflooring, several, more or less folded, Paleozoic strata, and a
subhorizontal substratum formed of secondary and tertiary deposits, themselves superimposed by several large quaternary zones and recent volcanic
massifs."
The Paleozoic sea makes its appearance in the northwest of the platform
as early as the Lower Cambrian stretching over the entire half of the western portion later on, and receding afterwards during the course of the
midcarboniferous.f During the Mesozoic, the great mesocretaceous transgression spreads widely over the northern part of the central and eastern
Sahara. Then, in the Tertiary the sea progressively recedes in the direction
of the northeast.
Basically, the geological formation of the platform can be summarized
as follows:
1. Precambrian metamorphic and granite subflooring, either flush
with the sedimentary formations of the substratum or forming it
2. Paleozoic (hercynian) series, more or less folded
3. Mesozoic and Tertiary layers, more or less tabular in shape
4. With, in addition, some superimposed Quaternary layers, including
a few recent volcanic series formations
* A geological bibliography of the north Africa and its surroundings, by Ph.
Morin, containing a great number of references was published in 1965, 1970, and
1973.
t Carboniferous is used by European geologists to designate both the Pennsylvanian
and Mississipian periods as a whole.
107
B. GEOLOGIC HISTORY
1. Geologic Boundaries
Geologically, the Sahara is bounded to the north by a large accidental
tectonic feature, stretching out from Agadir to the Gulf of Gabès, and to
the south by the valleys of the Senegal and of the Niger. A great number
of works relative to the geological study of the Sahara has been published*
(Kilian, 1922, 1925; Joléaud, 1938; Bernard, 1939; Monod, 1935, 1945;
Hernandez-Pacheco and Hernandez-Pacheco, 1942; Hernandez-Pacheco et
a/., 1949; Lelubre, 1952; Menchikoff, 1930, 1957; Pareyn, 1962; Freulon,
1964; Rognon, 1967; Furon, 1964, 1968; Conrad, 1969; Caby, 1970).
2. Relief of the Sahara
According to Menchikoff (1957): "The Sahara is a typical example of
a region of continental platform, composed of a Precambrian metamorphic subflooring, several, more or less folded, Paleozoic strata, and a
subhorizontal substratum formed of secondary and tertiary deposits, themselves superimposed by several large quaternary zones and recent volcanic
massifs."
The Paleozoic sea makes its appearance in the northwest of the platform
as early as the Lower Cambrian stretching over the entire half of the western portion later on, and receding afterwards during the course of the
midcarboniferous.f During the Mesozoic, the great mesocretaceous transgression spreads widely over the northern part of the central and eastern
Sahara. Then, in the Tertiary the sea progressively recedes in the direction
of the northeast.
Basically, the geological formation of the platform can be summarized
as follows:
1. Precambrian metamorphic and granite subflooring, either flush
with the sedimentary formations of the substratum or forming it
2. Paleozoic (hercynian) series, more or less folded
3. Mesozoic and Tertiary layers, more or less tabular in shape
4. With, in addition, some superimposed Quaternary layers, including
a few recent volcanic series formations
* A geological bibliography of the north Africa and its surroundings, by Ph.
Morin, containing a great number of references was published in 1965, 1970, and
1973.
t Carboniferous is used by European geologists to designate both the Pennsylvanian
and Mississipian periods as a whole.